Pressure actuated valve with improved biasing member

ABSTRACT

A valve for controlling material flow through a catheter, comprises a first flexible member including a first moveable element, wherein, when the first moveable element is in the open position, material may flow past the first flexible member through a first lumen of the catheter and, when the first moveable element is in the closed position, flow through the first lumen is prevented and a first biasing member coupled to the first flexible member for biasing the first moveable member toward the closed position.

BACKGROUND INFORMATION

Many medical procedures require repeated and prolonged access to apatient's vascular system. For example, during dialysis treatment bloodmay be removed from the body for external filtering and purification, tomake up for the inability of the patient's kidneys to carry out thatfunction. In this process, the patient's venous blood is extracted,processed in a dialysis machine and returned to the patient. Thedialysis machine purifies the blood by diffusing harmful compoundsthrough membranes, and may add to the blood therapeutic agents,nutrients etc., as required before returning it to the patient's body.Typically the blood is extracted from a source vein (e.g., the venacava) through a catheter sutured to the skin with a distal needle of thecatheter penetrating the source vein.

It is impractical and dangerous to insert and remove the catheter foreach dialysis session. Thus, the needle and catheter are generallyimplanted semi permanently with a distal portion of the assemblyremaining within the patient in contact with the vascular system while aproximal portion of the catheter remains external to the patient's body.The proximal end is sealed after each dialysis session has beencompleted to prevent blood loss and infections. However, even smallamounts of blood oozing into the proximal end of the catheter may bedangerous as thrombi can form therein due to coagulation which thrombimay then be introduced into the patient's vascular system when bloodflows from the dialysis machine through the catheter in a later session.

A common method of sealing the catheter after a dialysis session is toshut the catheter with a simple clamp. This method is oftenunsatisfactory because the repeated application of the clamp may weakenthe walls of the catheter due to the stress placed on the walls at asingle point. In addition, the pinched area of the catheter may not becompletely sealed allowing air to enter the catheter which may coagulateany blood present within the catheter. Alternatively, valves have beenused at the opening of the catheter in an attempt to prevent leakingthrough the catheter when the dialysis machine is disconnected. However,the unreliability of conventional valves has rendered themunsatisfactory for extended use.

SUMMARY OF THE INVENTION

The present invention is directed to a valve for controlling materialflow through a catheter, comprising a first flexible member including afirst moveable element, wherein, when the first moveable element is inthe open position, material may flow past the first flexible memberthrough a first lumen of the catheter and, when the first moveableelement is in the closed position, flow through the first lumen isprevented and a first biasing member coupled to the first flexiblemember for biasing the first moveable member toward the closed position.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a vascular access catheter;

FIG. 2 is a schematic drawing of a vascular access catheter inserted ina patient's vein;

FIG. 3 is a top elevation view of a valve device according to anexemplary embodiment of the present invention;

FIG. 4 is a top elevation view of a valve device according to anotherembodiment of the present invention;

FIG. 5 is a top elevation view of a valve device with double horizontalslits according to an embodiment of the present invention;

FIG. 6 is a top elevation view of a valve device with Y-configured slitsaccording to an embodiment of the present invention; and

FIG. 7 is a top elevation view of a valve device with a curved slitaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Semi-permanently placed catheters may be useful for a variety of medicalprocedures which require repeated access to a patient's vascular systemin addition to the dialysis treatments mentioned above. For example,chemotherapy infusions may be repeated several times a week for extendedperiods of time. For safety reasons, as well as to improve the comfortof the patient, injections of these therapeutic agents may be bettercarried out with an implantable, semi-permanent vascular accesscatheter. Many other conditions that require chronic venous supply oftherapeutic agents, nutrients, blood products or other fluids to thepatient may also benefit from implantable access catheters, to avoidrepeated insertion of a needle into the patient's blood vessels. Thus,although the following description focuses on dialysis, those skilled inthe art will understand that the invention may be used in conjunctionwith any of a wide variety of procedures which require long termimplantation of catheters within the body.

Examples of such implantable catheters include those manufactured byVaxcel™, such as the Chronic Dialysis Catheter and the ImplantableVascular Access System. These devices typically are inserted under thepatient's skin, and have a distal end which includes a needle used toenter a blood vessel. The devices also have a proximal end extendingoutside the body for connection with an outside line. Thesesemi-permanent catheters may be sutured to the patient's skin tomaintain them in place while the patient goes about his or her normaloccupations.

FIGS. 1 and 2 show an exemplary implantable catheter for kidneydialysis. Catheter 10 has a distal end 12 that is insertable under theskin and into the patient's vein, and which remains within the patient'sbody for the life of the catheter 10. For example, catheter 10 mayremain implanted in the patient for two years. As shown more clearly inFIG. 2 , distal end 12 fits within a vein 8 (e.g., the vena cava).During dialysis, blood from the patient is removed through a patientline such as catheter 10, and is purified by a dialysis machine (notshown) which is connected to hubs 18 and 20 of catheter 10 by a dialysisline. Catheter 10 in this example includes two lumens 22 and 24 whichare used respectively to remove blood from and reintroduce blood to thevessel 8. Lumen 22 terminates at an inflow tip 14 formed at the distalend 12 of the catheter 10 while lumen 24 terminates at an outflow tip 16formed at the distal end 12. Inflow tip 14 and outflow tip 16 areconnected to corresponding inflow and outflow hubs 18, 20, which areaccessible outside the body and which may be connected to external linesleading to and from the dialysis machine.

After the dialysis or other procedure has been completed, the catheter10 is disconnected from the dialysis machine, and is left within thepatient fluidly coupled to the patient's vascular system. When notconnected to a dialysis machine, the catheter 10 is securely sealed toprevent fluids and gases from crossing into the proximal end of catheter10 by preventing flow in and out of catheter 10 through hubs 18, 20. Aswould be understood by those skilled in the art, this sealing preventsthe risks associated with infections and thrombi which might beexperienced if air or other gas or liquid and/or pathogens were to passinto the catheter 10.

As indicated above, although conventional clamps or dips may be used toseal the catheter 10 between medical sessions, over time the wall of thecatheter 10 may be damaged in the area to which the clamp or clip isapplied. Sealing clamps or dips may also become dislodged during patientactivities, increasing the risk of leaks, infections, etc. Placing aclamp on the catheter 10 also increases the bulk of the distal end ofthe catheter which is exposed outside the patient's body, and mayadversely affect patient comfort.

Therefore, the catheter 10 includes one or more self sealing valvesalong each of the lumens 22, 24 to seal them when not being used duringdialysis and other transfusion or infusion sessions. For example, hubs18, 20 may be used to house one or more valves each of which is designedto seal the corresponding lumen 22, 24 under certain conditions, and toallow passage of fluids under other conditions. For example, in the caseof dialysis treatment, the system of valves may seal the catheter 10when it is not connected to an operating dialysis machine, and may allowboth an outflow of non-purified blood and an inflow of purified blood tothe patient when an operating dialysis machine is connected thereto.

Preferably, a valve system for use in such semi-permanent cathetersshould, when in the open position, allow a flow rate therethrough whichis sufficient to allow the procedure to be completed in an acceptablyshort time. When in the closed position, the valve should completelyseal the catheter. That is, if the valve requires excessive force to beopened, the flow rate through the catheter may be reduced to the pointwhere the time required for the procedure is unacceptably extended. Inaddition, a valve system having moving parts of too great a bulk mayalso result in larger blockages within the catheter or the hub housingthe valve thereby reducing the flow rate through the catheter. Themechanism that moves the valve into the open and closed positions mayblock the flow through the valve if it protrudes into the flow passage,and thus the size and bulk of the mechanism should preferably beminimized to avoid impeding flow through the open valve.

The portion of the valve that moves to the open position must alsocompletely return to the closed position when the session is completed.For example, a pressure sensitive valve may be used, which opens inresponse to a pressure driving the flow through the catheter. In thecase of a dialysis catheter, the valve or valves may open when apressure generated by the dialysis machine exceeds a predeterminedthreshold to allow circulation and purification of the patient's blood.When the dialysis machine is turned off and the pressure in the dialysisline is reduced below the threshold, the valve is completely sealed toprevent further flow from and to the patient. Some pressure is alsopresent in the patient line connecting the valve to the patient's veinas a result of the circulation in the patient's vascular system. Each ofthe valves must therefore be designed so that it will not respond tosuch pressure variations introduced by the vascular system and will notopen unless a pressure above the threshold is generated externally, forexample, by a dialysis machine.

The exemplary embodiments according to the present invention describedherein obtain both a secure closure of a semi-permanent catheterimplanted in a patient when the catheter is not in use and permit a flowpassage that is easily opened to allow a sufficient flow rate whenaccess to the vascular system is necessary.

In many applications, the pressure actuated valve system remains openfor the entire length of a therapeutic session, which may last asignificant amount of time. For example, in the case of a dialysissession, the valve system may remain open for up to four hours at atime, during sessions carried out up to three times a week. Theexemplary embodiments of valves according to the present inventionprovide a seal to the catheter even after being maintained in the openposition for prolonged periods of time.

Specific embodiments of the present invention will be described belowwith reference to the drawings. FIG. 3 shows a top plan view of anexemplary embodiment of a valve element 100 used to control the flowthrough a medical tube such as the catheter 10 of FIG. 1 . For example,valve element 100 may be located in a flow passage within a valvehousing formed in either or both of the hubs 18, 20, through whichfluids flow to and from the distal end 12. As will be apparent to thoseskilled in the art, the valve housing may be placed at any otherlocation along the length of catheter 10 and may be unitary with thecatheter 10, or may be formed as a separate component. In addition, itwill be apparent that a single valve housing with dual flow passages andone valve 100 within each of the flow passages may be provided insteadof two separate valve housings for the hubs 18, 20, respectively, toindependently control fluid flow in each direction. Inflow to thepatient may take place via one of the dual flow passages of the singlehub, and outflow from the patient via the other flow passage.

In the exemplary embodiment shown in FIG. 3 , the valve element 100 isformed as a flexible disk 110 having dimensions appropriate to the sizeof the flow passage within the one of the hubs 18, 20 into which it isto be mounted. The flexible disk 110 may be formed of any sufficientlyflexible material, such as a polymeric material. More specifically, theflexible disk 110 may be formed of silicone. The flexible disk 110 mayalso include a peripheral portion 116 adapted to be connected to aninner surface of the flow passage to seal perimeter of the flow passagearound flexible disk 110. The valve element 100 includes a slit 112which is extends through the entire thickness of the flexible disk 110.The slit 112 separates two movable elements 118 from one another to forman openable portion of the disk 110 which creates a flow passagetherethrough when the movable elements 118 are placed in an openposition separated from one another. For example, when the edges 120 ofthe movable elements 118 are moved out of the plane of the flexible disk110, an opening through the flexible disk 110 is formed along the slit112. In this exemplary embodiment, the movable elements 118 are formedas resilient flaps substantially constrained in all directions exceptalong the slit 112. Accordingly, the elements 118 are substantiallyconstricted and may only move along the edges 120 to form a relativelysmall opening.

In one exemplary embodiment the valve element 100 is used in conjunctionwith dialysis equipment, and movement of movable elements 118 to theopen position is prompted by an actuating pressure of a fluid withindialysis lines 30, 32 which may be connected to the hubs 18, 20,respectively, to connect the catheter 10 to a dialysis machine. Inparticular, an actuating pressure is generated by pumps in the dialysismachine to move the patient's blood between the patient and thefiltration equipment. Although the movable elements 118 are formed asflexible flaps, they are formed with a predetermined amount ofresilience to allow them to remain in the closed position when not actedupon by the pressure in dialysis lines 30, 32. Specifically, theelements 118 are biased to remain in the closed position abutting oneanother along edges 120 at all times when they are not acted on by apressure outside a range of approximately 22 to 44 mmHg. Specifically,as mentioned above, the elements 118 are formed so that the amount ofresilience is sufficient to maintain them in the closed position withoutbeing forced open by fluid forces generated by natural circulation ofthe patient's blood. As would be understood by those skilled in the art,the amount of pressure required to open the movable elements 118 is afunction of the resilience of the material forming those elements, thesize and shape of the slit 112, and the size of the flow passagecontaining the valve element 100. The details of the geometry of theslit 112 and the movable elements 118 may be selected to obtain thedesired characteristics of maximum flow in the open position, and toensure that valve element 100 seals the flow passage when the pressureis removed.

A stiffening element 114 may be included in valve element 100, to bettercontrol the amount of force biasing the movable elements 118 to theclosed position. In particular, coupling a stiffening element to anotherwise flexible disk 110 (or forming a stiffening element integrallytherewith) provides a valve element 100 including movable elements 118more resistant to plastic deformation during sessions lasting multiplehours in which the valve element 100 is kept open. An example of asuitable stiffening member is the addition of stiffening ring 114 to theflexible disk 110. The stiffening element 114 may, for example, beformed of a wire embedded within the valve element 100. Of course, thoseskilled in the art will understand that the stiffening element 114 maybe formed of metal, plastic or any substantially rigid material.

In one exemplary embodiment, the stiffening ring 114 may be embeddedwithin the material of the disk 110, to minimize the bulk of thecombination. In different embodiments, stiffening elements may be bondedto one or both sides of the valve element 100, depending on therequirements of the use of the valve element 100. The shape of thestiffening elements used in the valve element 100 may also be modified,depending on the desired characteristics of the force urging the movableelements 118 to the closed position. Alternatively, the stiffeningelements may be integrally formed with the disk 110.

As indicated above, the maximum flow that can pass through valve element100 and the ability to close fully when the actuating pressure isremoved are important design parameters for the pressure actuated valvesdescribed herein. According to embodiments of the invention, thesedesign parameters may be controlled by properly shaping and sizing theslit or slits 112. Selection of the dimensions of the slit 112 resultsin movable elements 118 having a desired shape and being constrainedalong selected edges. In the exemplary embodiment shown in FIG. 3 , alinear slit having a width d of approximately 0.002 inches and a lengthof approximately 0.150 to 0.280 inches is provided in the center of anoval flexible disk 110 extending along a major axis of the disk. Theflexible disk 110 could have a thickness of approximately 0.015 to 0.030inches and could be manufactured from silicone, as a result its surfaceresistivity rating would be approximately 35 to 70 A. The movableelements 118 used in this configuration are flaps that form an openingby deflecting away from the plane of the disk 110 due to theirflexibility, since they are constrained along all sides except along theslit 112. This configuration provides satisfactory performance in adialysis catheter application, with the catheter having conventionaldimensions and providing conventional flow rates. For example, thepressure to which the valve may be subjected during dialysis may be inthe range of 200 to 285 mmHg while the pressures applied to the valve bythe patient's vascular system are expected to remain below 22 mmHg.Thus, the valve system will preferably be designed to remain sealed whennot subjected to a pressure of at least 44 mmHg and, when subjected tothe a pressure above that threshold should preferably allow a flow rateof at least 300 ml/min and more preferably at least 350 ml/min withoutsubstantially failing to meet these criteria during a life span of oneor more years while being subjected to 3 or more uses of up to 4 hourseach per week.

The performance characteristics of the valve element 100 can be furthertuned by selecting an appropriate length l of the slit 112. By alteringthis length l, both the maximum flow rate and the opening/closingperformance of the valve element 100 will be changed. For example,increasing the length of the slit 112, other parameters being the same,increases a maximum size of the opening through the flexible disk 110,and makes it easier to displace the movable elements 118 to the openposition as they are unconstrained along longer edges 120. For the samereason, the movable elements 118 are subjected to a reduced forcebiasing them toward the closed position when the actuating pressure isremoved. Both the width d and the length l of the silt 112 are selectedas a tradeoff between ease/size of the opening and the biasing forceclosing the valve element 100 after use.

A different exemplary configuration of slits to define the movableelements is shown in FIG. 4 . In this embodiment, a flexible disk 210 isprovided with slits 212, 214 in a substantially H-shaped configurationthat define movable elements 218. The slit 212 is a substantially linearslit aligned with a major dimension of the disk 210, and the slits 214extend substantially perpendicular to slit 212, disposed nearterminating points thereof. This configuration of slits permits themovable elements 218 to more easily move to the open configuration,since each movable element 218 is unconstrained along both the slit 212and the slits 214. The pressure generated by an external pump, such as adialysis pump, thus can more easily force the movable elements 218 tothe open position. The two additional unconstrained sides of the movableelements 218 also form a larger open area of flexible disk 210, so thata greater flow rate can pass through the valve element 200.

Additional resilient elements may also be used in the exemplaryembodiment shown in FIG. 4 to achieve desired closing characteristics ofthe valve element 200. For example, a pair of resilient elements 220 maybe disposed substantially parallel to the slit 212 on either sidethereof. The resilient elements 220 control the deflection and provide aforce biasing the movable elements 218 toward the closed position alongthe axis of the slit 212. Those skilled in the art will understand thatadditional resilient elements 222 may be used to increase the biasingforce and/or to control the deflection of the movable elements 218 alongan axis parallel to the slits 214. This exemplary combination ofH-configured slits and corresponding H-configured resilient elementsresults in a high flow, easily opened pressure actuated valve element200, which is able to completely return to the closed position once theactuating pressure is removed. This configuration also resists plasticdeformation that may occur when valve elements are kept in the openposition for extended periods of time, and which may prevent the valvefrom fully closing due to retaining a “memory” of the open position.

Another exemplary embodiment according to the present invention isdepicted in FIG. 5 . In this embodiment, a double horizontal slit isused to define the movable elements of a valve element 250. Morespecifically, a pair of substantially parallel slits 262 extend throughthe flexible disk 260, substantially along a major dimension thereof. Inthe case of a substantially elliptical flexible disk 260, as shown, theslits 262 are substantially parallel to a major axis of the ellipse. Amovable element 264 is thus defined substantially at the center of theflexible disk 260, and is constrained only at ends 265 thereof neartermination points of the slits 262.

The greater unconstrained length of the sides of the movable element 264along the slits 262, enables a large flow area to open as a result of anactuating pressure. For the same reason, a relatively low actuatingpressure is needed to open the movable element 264. To ensure a completeclosing of the valve element 250 when the actuating pressure is removed,for example, resilient elements may be added around the slits 262 tofurther bias the movable element 264 to the closed position. In theexemplary embodiment shown in FIG. 5 , resilient elements 266, 268,which may comprise, for example, wires embedded within the valve element250, are disposed in a substantially rectangular configurationsurrounding the slits 262. In this configuration the resilient elements266, 268 control the deflection of the movable element 264 in directionssubstantially parallel and perpendicular to the slit orientation andprovide a biasing force that closes the movable element 264 when theactuating pressure is removed. The resilient elements 266, 268 may forma complete rectangle, or may be separated at the vertices.

FIG. 6 shows yet another embodiment of the pressure actuated valveaccording to the present invention. In this exemplary embodiment, alinear slit is combined with a pair of Y-configured slits to provide alarger flow area when a valve element 300 is placed in the open positionby an actuating pressure thereagainst. As shown in the drawing, thevalve element 300 is formed as a flexible disk 310 which, in thisexample, has a substantially elliptical shape. It will be apparent tothose skilled in the art that different shapes of the flexible disk 310may be used, depending on the shape and dimensions of the housing withinwhich the valve element 300 is to be placed. A substantially linear slit312 is formed in the flexible disk 310, for example along a majordimension thereof, and is complemented by two pairs of slits 314. Afirst pair of the slits 314 is disposed at a first end of the slit 312with a second pair of slits 314 being formed at the second end of theslit 312. The slits 314 are formed at an angle with the slit 312, sothat, at each end of the slit 312, a substantially Y-shapedconfiguration of slits is formed.

In the exemplary embodiment shown, the slits 312 and 314 do not touchone another so that the movable elements 320 are continuous withportions 322 of the flexible disk 320. In different embodiments, theslits 312 and 314 may intersect with one another, breaking the flexibledisk 320 into additional distinct moving elements. In the exemplaryembodiment shown, the movable elements 320 are unconstrained along theslits 312, 314, but are constrained in the region between the slits bybeing continuous with the portions 322 of the flexible disk 320. Theaddition of the Y-configured slits permits the movable elements 320 toopen to a greater extent under an equivalent actuating pressure, whileretaining a biasing force sufficient to completely close the openingwhen the actuating pressure is removed. To further bias the movableelements 320 toward the closed position, resilient elements 316, 318 maybe added. As discussed in the context of previous embodiments, theresilient elements 316, 318 may be disposed in a substantiallyrectangular pattern around the slits 312, 314 to control the deflectionand closure of the movable elements 320 in two directions substantiallyperpendicular to one another. The resilient elements 316, 318 may form acompletely rectangular enclosure as shown in FIG. 6 , or may have openvertices, as shown in previous embodiments. As would be understood bythose skilled in the art, the relative size and orientation of the slits312, 314 may be selected to give desired flow and closing properties,for a given flexible disk 320.

A different exemplary embodiment according to the present invention isdepicted in FIG. 7 . In this example, a valve device 350 comprises aflexible disk 360 having a slit 362 formed therein. The slit 362 is notformed as a linear slit, but instead is curved about a principal axis ofthe flexible disk 360. In the example shown in FIG. 7 , the slit 362follows a substantially sinusoidal path. However other curved paths maybe used with similar effect. The sift 362 defines two movable elements364, 366 which are complementary to each other along the slit 362. Abenefit of this configuration is that for a given length l of the slit362, a larger opening area of the valve device 350 is obtained ascompared to linear slit designs. Since the unconstrained edges of themovable elements 364, 368 are longer due to their curved shape of theslit 362, a given actuating pressure displaces a larger portion of themovable elements 364, 366 to the open position. Thus, this design allowsa larger flow area through the valve device 350.

As was the case in other the exemplary embodiments of the invention, theresilience of the movable elements 364, 366 is controlled to ensure thatthe valve element 350 fully closes once the actuating pressure isremoved—even after remaining open for extended periods of time (i.e., toensure that the valve is not subject to “memory” effects). Accordingly,the resilience of the material forming the movable elements 364, 366 ispreferably selected and additional resilient elements are incorporatedinto the flexible disk 360, as described above with respect to otherembodiments, based on the conditions to which the valve element 350 isto be subjected to ensure that such plastic deformation does not resultin degraded performance over time.

The present invention has been described with reference to specificexemplary embodiments. Those skilled in the art will understand thatchanges may be made in details, particularly in matters of shape, size,material and arrangement of parts. For example, different flexible disksmay be used to form the pressure sensitive valve, and may have differentdimensions than those shown. Accordingly, various modifications andchanges may be made to the embodiments without departing from thebroadest scope of the invention as set forth in the claims that follow.The specifications and drawings are, therefore, to be regarded in anillustrative rather than a restrictive sense.

What is claimed:
 1. A valve comprising: a flexible member comprising afirst moveable element, a second movable element, and at least onebiasing member; wherein the first moveable element and the secondmoveable element are configured to remain in a closed position whenacted upon by a predetermined fluid pressure; and wherein the at leastone biasing member is configured to bias the first moveable element andthe second moveable element towards the closed position.
 2. The valve ofclaim 1, wherein the predetermined threshold level of fluid pressure isbelow 44 mmHG.
 3. The valve of claim 1, wherein the first moveableelement and the second moveable element are configured to move to anopen position when acted upon by a flow of fluid above the predeterminedfluid pressure.
 4. The valve of claim 1, wherein the valve is sized tofit within a flow passage of a catheter hub.
 5. The valve of claim 4,wherein the flexible member is substantially an elliptical shape.
 6. Thevalve of claim 1, wherein the valve is configured to allow a flow rateof up to 350 ml/min.
 7. The valve of claim 1, wherein the at least onebiasing member is integrally formed within the flexible member.
 8. Thevalve of claim 7, wherein the at least one biasing member comprises twobiasing members both comprised of a plastic material.
 9. The valve ofclaim 7, wherein the at least one biasing member comprises two biasingmembers both comprised of a metal material.
 10. The valve of claim 7,wherein the at least one biasing member is configured to control theamount of force biasing the first moveable element and the secondmoveable element towards the closed position.
 11. The valve of claim 1,wherein the flexible member comprises a major axis.
 12. The valve ofclaim 11, wherein the first movable element and the second movableelement are configured to be substantially parallel to the major axis.13. A valve comprising: a flexible member comprising a first moveableelement, a second movable element, and two biasing members; wherein thefirst moveable element and the second moveable element are configured toremain in a closed position when acted upon by a predetermined fluidpressure; and wherein the two biasing members are configured to bias thefirst moveable element and the second moveable element towards theclosed position; and wherein the two biasing members are integrallyformed within the flexible member.
 14. The valve of claim 13, whereinthe predetermined threshold level of fluid pressure is below 44 mmHG.15. The valve of claim 13, wherein the flexible member is substantiallyan elliptical shape.
 16. The valve of claim 13, wherein the flexiblemember comprises a major axis.
 17. The valve of claim 16, wherein thefirst movable element, the second movable element, and the biasingmember are configured to be substantially parallel to the major axis.18. A valve comprising: a flexible member comprising a first moveableelement, a second movable element, and a biasing member; wherein thefirst moveable element and the second moveable element are configured toremain in a closed position when acted upon by a fluid flow below apredetermined fluid pressure; and wherein the biasing member isconfigured to bias the first moveable element and the second moveableelement towards the closed position; wherein the biasing member isintegrally formed within the flexible member; and wherein the flexiblemember is substantially elliptically shaped comprising a major axis. 19.The valve of claim 18, wherein the first movable element, the secondmovable element, and the biasing member are configured to besubstantially parallel to the major axis.
 20. The valve of claim 18,wherein the flexible member further comprises a slit.